Many of drugs, particularly anticancer drugs, are hydrophobic compounds that mostly do not dissolve in water. In order to obtain a desired therapeutic effect using such a drug, usually, the drug is solubilized and administered to a patient. Therefore, solubilization of a sparingly water-soluble drug, particularly a sparingly water-soluble anticancer drug, is important for oral or parenteral preparations, particularly preparations for intravenous administration.
As one of the methods for solubilizing a sparingly water-soluble anticancer drug, a method of adding a surfactant may be used. For example, it is known to use a polyoxyethylene castor oil derivative (Cremophor) for solubilizing paclitaxel. Furthermore, regarding other methods, methods of using a micelle-forming block copolymer as a drug carrier is described in Patent Document 1, Patent Document 2, Patent Document 3, and the like. Patent Document 4, Patent Document 5, and Patent Document 6 describe paclitaxel-encapsulated micelles that use block copolymers having polyethylene glycol (PEG) structural moieties and polyamino acid structural moieties, as drug carriers.
Patent Document 5 describes that paclitaxel-encapsulated micelles having a dominantly high antitumor effect are obtained by altering the structure of the polyamino acid structural moiety of the block copolymer that forms the micelles used in Patent Document 4.
Patent Document 6 describes that when a production method different from that of Patent Document 5 is used, the amount of residual carboxylic acid structures in the structure of the polyamino acid structure moiety of the block copolymer that forms micelles is decreased, and toxicity is decreased as compared with the paclitaxel-encapsulated micelles described in Patent Document 5.